The present invention relates to a printer with a recording head capable of ejecting an ink drop, and more particularly to a called bi-directional printer capable of printing on a printing medium in both a forward scan and a reverse scan by the recording head.
In the printer with a recording head for ejecting an ink drop, there are proposed techniques to curb an elongation of a printing time, which results from the size increase of a printing medium and the definition increase of a print image. An example of the technique is a bi-directional printing technique in which the printer prints on a printing medium in both the scanning directions of a forward scan and a reverse scan, which are performed by the recording head.
In the printer using such a technique, i.e., the called bi-directional printer, when an ink drop is ejected at the same timing (same ejection positions) in both the forward scan and the reverse scan, printing positions in the forward and reverse scans are off-set from each other. As shown in FIG. 19A, an ink ejection direction is expressed by a composite vector of a vector Vm, Vmxe2x80x2 (moving velocity vector) representative of a moving velocity of the recording head 1003 and a vector Vj (ejecting velocity vector) representative of an ink ejecting velocity of an ink drop ejected from the recording head 1003. Where the timing of ejecting an ink drop in the forward scan F is the same as that of ejecting an ink drop in the reverse scan R, the direction of ejecting an ink drop in the forward scan will be different from that in the reverse scan since a direction of the moving velocity Vm of the recording head in the forward scan is different from direction of the moving velocity Vmxe2x80x2 in the reverse scan. As a result, a printing position on the printing medium in the forward scan is different from that in the reverse scan (PO in the figure).
To cope with this, in design, an ink ejection position JP in the forward scan F is off-set from that JPxe2x80x2 in the reverse scan R so as to secure the coincidence of the printing positions in the forward scan and in the reverse scan at PP as shown in FIG. 19B. Further, a function to print a test pattern, which is used for detecting a printing-position off-set between the forward scan and the reverse scan is incorporated into the printer. To correct the printing-position off-set, an operator prints out the test pattern. He adjusts elevation of the recording head 1003 and the platen 1002 while referring the print result of the test pattern, to thereby set up a proper distance from the ink ejecting surface of the recording head to the printing surface of the printing medium 1001.
Precision improvement in the paper feeding/discharging mechanism of the recent printer enables the printer to print on various types of printing media. Where the bi-directional printer prints on various types of printing media, the apparatus will meet the medium thickness difference. When the medium thickness difference exists, the distance from the ink ejecting surface of the recording head to the printing surface of the printing medium inevitably changes. An influence of the distance change upon the printing-position off-set is not negligible.
Let us consider a case where identical images are formed on a normal paper sheet and a post card (1010 in FIG. 19B). In this case, the normal paper sheet has a thickness of about 0.1 mm thick and the post card has a thickness of about 0.2mm. One of the normal paper sheet and the post card (or a printing medium having a thickness value between those values of them) is used for a reference for correcting the printing-position off-set, and the distance from the ink ejecting surface of the recording head to the printing surface of the printing medium is adjusted to as to correct the off-set. Then, the printer prints on the other sheet (both the sheets when the printing medium of the medium thickness is used for the reference). In this case, an off-set of the printing position in the forward scan from the printing position in the reverse scan is not so distinguished.
Let us consider another case where identical images are printed on thick printing media of about 1.5 mm thick, such as label sheets and thick sheets, in addition to the normal paper sheets and the post cards. The normal paper sheet or the post card is used for a reference for correcting the printing-position off-set, and the distance from the ink ejecting surface of the recording head to the printing surface of the printing medium is adjusted to as to correct the off-set. In this case, a great printing-position off-set POxe2x80x2 is created when the printer prints on those thick printing media (1011 in FIG. 19B).
The related bi-directional printer is not designed such that it can handle various types of printing media of different thickness values. To correct the printing-position off-set, the related printer takes the following tasks: every time a printing medium having a different thickness is set to the printer, a test pattern is printed on the printing medium set anew; and an operator adjusts a position of the platen and/or recording head on the basis of the print result of the test pattern to set up a proper distance from the ink ejecting surface of the recording head to the printing surface of the printing medium. Following those tasks, the printer prints on the printing medium. The execution of those tasks is complicated and troublesome, and imposes heavy on the operator.
A viscosity of ink varies with variation of temperature. A variation of the viscosity of ink results in a velocity of ejecting an ink drop from the recording head. Normally, the recording head per se has a temperature-dependency. Therefore, when temperature of the recording head varies, the ink ejecting velocity also varies. Thus, an ink ejection direction is expressed by a composite vector of the moving velocity vector of the recording head and the ejecting velocity vector of the ejecting ink drop. Therefore, when the ink ejecting velocity varies, the ink ejecting direction varies. This yields a printing-position off-set between the forward scan and the reverse scan.
Some of recent bi-directional printer are capable of printing on a printing medium of large size, e.g., A0. To print on a large size printing medium by use of the bi-directional printer, the printing is contiguously performed for a relatively long time. During the long printing operation, temperature of the recording head varies and an ink ejecting direction varies. Therefore, the following expedience is inevasible. Even if the ink-ejection timing is corrected so as to eliminate the printing-position off-set between the forward and reverse scans by the recording head before printing on the printing medium starts, a temperature variation of the recording head during the printing operation inevitably yields a printing-position off-set between the forward and reverse scans.
For the above background reasons, the present invention is made and has an object to lessen stress imposed upon the operator when bi-directional printing on various types of printing media are carried out. The invention has another object to obviate a printing-position off-set between the forward scan and the reverse scan, which arises from the temperature-dependency of the recording head and ink used.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a printer capable of printing on a printing medium in both a forward scan and a reverse scan by a recording head for ejecting ink drops, comprising- interface means for acquiring control information containing at least information on a thickness of the printing medium; and timing correction means for correcting timings of ejecting ink drops toward the printing medium during at least one of the forward and reverse scans in accordance with the thickness information of the printing medium contained in the control information acquired by the interface means.
The interface means may be input means, e.g., an operation panel, for receiving control information entered by an operator: It may be a variety of sensors for sensing temperature and sheet thickness or means for acquiring control information from a print controller (for transmitting print data) connected to a printer by way of a communication line.
The printer acquires control information automatically or an operator by use of the interface means. The timing correction means corrects timings of ejecting ink drops toward the printing medium during at least one of the forward and reverse scans in accordance with a distance from an ink ejecting surface of the recording head to a printing surface of the printing medium, which the distance is determined by the thickness information of the printing medium contained in the control information acquired by the interface means. An advantageous feature of the thus constructed printer is to lessen stress imposed to the operator when comparing with a case where the related bi-directional printer prints on various types of printing media of different thickness in a bi-directional printing mode.
Preferably, the control information contains information on an ink ejecting velocity and information on a moving velocity of the recording head. The timing correction means corrects timing of ejecting ink drops to the printing medium in accordance with a distance from an ink ejecting surface of the recording head to a printing surface of the printing medium, which the distance is determined by the thickness information of the printing medium contained in the control information received from the print controller, and an ink ejecting direction specified by the information on the ink ejecting velocity and the moving velocity of the recording head.
This technical feature advantageously operates in a situation where an ink ejecting velocity and a moving velocity of the recording head are varied in accordance with a sort of printing medium to be used. In this situation, a timing of ejecting an ink drop on a printing medium can be corrected so as to correct a printing-position off-set between the forward and reverse scans. Thus, the printing-position off-set can be corrected with high precision.
According to a second aspect of the present invention, there is provided a printer capable of printing in both a forward scan and a reverse scan by a recording head for ejecting ink drops, comprising: storing means for storing a mathematical expression describing a relation of a thickness of the printing medium with an ejection-timing correction quantity during at least one of the forward and reverse scans; correction-quantity calculating means for calculating an ejection-timing correction quantity dependent on a thickness of the printing medium to be under printing by use of the expression; and timing control means for controlling a timing to eject an ink drop onto the printing medium to be under printing in at least one of the forward and reverse scans in accordance with an ejection-timing correction quantity calculated by the correction-quantity calculating means.
The printer may include means, e.g., an operation panel, for receiving the medium-thickness information entered by an operator. The thickness information of the printing medium to be under printing may be acquired by use of the reception means. Alternatively, it may be received from a print controller (for transmitting print data) connected to a printer by way of a communication line. In a second alternative, the medium thickness information may be acquired by use of a sensor, which is provided for detecting a thickness of a printing medium set on a platen.
In the printer, a mathematical expression is prepared in advance which describes a relation between a thickness of a printing medium, which specifies a distance between the ink ejecting surface of the recording head and the printing surface of the printing medium, and an ejection-timing correction quantity in at least one of the forward and reverse scans. The printer calculates an ejection-timing correction quantity which is dependent on a distance between the ink ejecting surface of the recording head and the printing surface of the printing medium, which the distance is specified by a thickness of a printing medium to be under printing, by use of the expression, and corrects a timing of ejecting an ink drop to the printing medium in at least one of the forward and reverse scans in accordance with the calculated ejection-timing correction quantity.
With the use of the mathematical expression, the printer corrects an off-set of the printing position in the forward scan relative to that in the reverse scan, which arises from the bi-directional printing applied to various types of printing media of different thickness. Therefore, the thus constructed printer is capable of lessening stress imposed to the operator when comparing with a case where the related bi-directional printer prints on various types of printing media of different thickness in a bi-directional printing mode.
The ejection-timing correction quantity for a thickness of a printing medium to be under printing is calculated by use of the mathematical expression prepared in advance. Because of this, a memory capacity of the memory for storing the ejection-timing correction quantity may be reduced when comparing with a case of storing in advance the ejection-timing correction quantities prepared for various types of printing media of different thickness.
The mathematical expression may be constructed by calculating ejection-timing correction quantities to correct printing-position off-set each between the forward scan and the reverse scan at least two different distances each from the ink ejection surface of the recording head to the printing surface of the printing medium.
The mathematical expression is expressed by   D  =                                          D            1                    -                      D            2                                                H            1                    -                      H            2                              ⁢      H        +                                        D            1                    ⁢                      H            2                          -                              D            2                    ⁢                      H            1                                                H          2                -                  H          1                    
where
D: ejecting-timing correction quantity to be calculated;
H: distance from the ink ejection surface of the recording head to the printing surface of the printing medium to be under printing (viz., the printing medium for which the ejection-timing correction quantity is to be calculated) (The distance H is determined by a printing medium to be under printing.);
D1: ejecting-timing correction quantity when a distance from the ink ejection surface of the recording head to the printing surface of the printing medium is H1; and
D2: ejecting-timing correction quantity when a distance from the ink ejection surface of the recording head to the printing surface of the printing medium is H2.
For example, when a distance (platen gap) from the ink ejecting surface of the recording head to the platen is fixed at P, the printer prints on two types of printing media (reference sheets) of different thickness values T1 and T2, and calculates ejection-timing correction quantities D1 and D2 to correct the printing-position off-set between the forward scan and the reverse scan for the reference sheets. Here, the distance from the ink ejecting surface of the recording head to the printing surface of the printing medium is equal to the result of subtracting a thickness of the printing medium from the platen gap. The above mathematical expression can be arranged into   D  =                                          D            1                    -                      D            2                                                (                          P              -                              T                1                                      )                    -                      (                          P              -                              T                2                                      )                              ⁢              (                  P          -          T                )              +                                        D            1                    ⁡                      (                          P              -                              T                2                                      )                          -                              D            2                    ⁡                      (                          P              -                              T                1                                      )                                                (                      P            -                          T              2                                )                -                  (                      P            -                          T              1                                )                    
where
T: thickness of a printing medium to be under printing (viz., the printing medium for which the ejection-timing correction quantity is to be calculated).
For example, when the platen gap may be set to P1 or P2 by moving the platen or the recording head, the printer prints a printing medium (reference sheet) of a thickness value T1 at the platen gaps P1 and P2 in a bi-directional printing mode, and calculates ejection-timing correction quantities D1 and D2 to correct the printing-position off-sets each between the forward scan and the reverse scan. Since the distance from the ink ejecting surface of the recording head to the printing surface of the printing medium is equal to the result of subtracting the medium thickness from the platen gap, the above mathematical expression may be arranged into   D  =                                          D            1                    -                      D            2                                                (                                          P                1                            -                              T                1                                      )                    -                      (                                          P                2                            -                              T                1                                      )                              ⁢              (                  P          -          T                )              +                                        D            1                    ⁡                      (                                          P                2                            -                              T                1                                      )                          -                              D            2                    ⁡                      (                                          P                1                            -                              T                1                                      )                                                (                                    P              2                        -                          T              1                                )                -                  (                                    P              1                        -                          T              1                                )                    
where
P: platen gap value (P1 or P2) used for printing on the printing medium to be under printing.
According to a third aspect of the present invention, there is provided a printer capable of printing on a printing medium in both a forward scan and a reverse scan by a recording head for ejecting ink drops, comprising: temperature detecting means for detecting temperature of the recording head; and timing correction means for correcting a timing of ejecting an ink drop to the printing medium in at least one of the forward and reverse scans in accordance with the temperature of the recording head detected by the head temperature detecting means.
The printer detects temperature of the recording head by temperature detecting means. The timing correction means corrects a timing of ejecting an ink drop to the printing medium in at least one of the forward and reverse scans in accordance with an ink ejecting direction to the printing medium, which is specified by the temperature of the recording head detected by the head temperature detecting means. Therefore, the printer can obviate a printing-position off-set between the forward scan and the reverse scan, which arises from the temperature-dependency of the recording head and ink used.
The printer may include home-position detecting means for detecting that the recording head reaches a home position. In this case, when the home-position detecting means for detecting that the recording head reaches a home position, the timing correction means corrects a timing of ejecting an ink drop to the printing medium in at least one of the forward and reverse scans in accordance with the temperature of the recording head detected by the head temperature detecting means.
Accordingly, every time the recording head reaches the home position, the ink ejection timing is corrected in accordance with a head temperature at that time. In other words, every time the recording head moves forward and returns to the home position, the ink ejection timing is corrected on the basis of the newest recording head temperature. Therefore, the printer can obviate a printing-position off-set between the forward scan and the reverse scan in the bi-directional printing mode.